Double-stranded RNA molecules (dsRNA) have been shown to block gene expression in a highly conserved regulatory mechanism known as RNA interference (RNAi). WO 99/32619 (Fire et al.) discloses the use of a dsRNA of at least 25 nucleotides in length to inhibit the expression of genes in C. elegans. dsRNA has also been shown to degrade target RNA in other organisms, including plants (see, e.g., WO 99/53050, Waterhouse et al.; and WO 99/61631, Heifetz et al.), Drosophila (see, e.g., Yang, D., et al., Curr. Biol. (2000) 10:1191-1200), and mammals (see WO 00/44895, Limmer; and DE 101 00 586.5, Kreutzer et al.). This natural mechanism has now become the focus for the development of a new class of pharmaceutical agents for treating disorders that are caused by the aberrant or unwanted regulation of a gene.
Despite significant advances in the field of RNAi and advances in the treatment of pathological processes, there remains a need for formulations that can selectively and efficiently deliver agents to cells where silencing can then occur.
While delivery of oligonucleotides across plasma membranes in vivo has been achieved using vector-based delivery systems, high-pressure intravenous injections of oligonucleotides and various chemically-modified oligonucleotides, including cholesterol-conjugated, lipid encapsulated and antibody-mediated oligonucleotides, to date, delivery remains the largest obstacle for in vivo oligonucleotide therapeutics.